Question about 2004 Chevrolet TrailBlazer

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2003 Chevrolet Trailblazer 4.2L I6 76K miles - started pulling a code for a misfire on cylinder 5; replaced coil for that cylinder and replaced all spark plugs. It runs worse now and is pulling the P0300 multiple/random cylinder misfires. Service Engine Soon light is on and blinking. Any suggestions would be helpful; doesn't seem like the converter is plugged. Thanks,

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With a service engine light blinking...don't drive it.

When replacing the spark plugs, double check that the boots on the coils are installed correctly. Check these again, and make sure to either listen for or feel a little click which tells you it's properly seated on the top of the spark plug. This is a common thing, happens all the time to people with TB's and Envoys. I've even done this myself.

In case you didn't know, # 1 cylinder is up front near the fan, then it runs in order to #6 at the firewall. Possibility....(don't take this as doubting you), maybe the wrong coil was replaced and one or more coil boots weren't set properly? Some things to check anyway.

Posted on Mar 25, 2011


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Pull the coil plugs when running. One at a time. If the engine gets worse the coil is good. No difference. Most likely the coil is bad. To check it again, swap it with another. Pull the plug on the suspected bad one. If it gets worse, look to wiring at the one that was no deference. Check for power to the plug.

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Your checking for codes & throwing parts at it

Your NOT diagnosing anything like the cylinder
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Recommend replace plugs (o.e.delco) and #4 coil and recheck.

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try replacing or cleaning the injectors
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I changed the plugs and wires on my 2003 trailblazer. I gapped the spark plugs @ .040 and checked all of the connections. Now my engine skips. It gave a 0300 code ( multiple cylinder misfire). Any...

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This is a random/multiple cylinder misfire. Last time I had this problem, it was my coils. Try checking your coils first.

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1 Answer

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Could indicate a burnt or warped valve, a worn cam lobe, or it may be pumping oil to the top of the cylinder and drowning or accumulating on the spark plug.

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